Modeling tidal sand wave recovery after dredging: effect of different types of dredging strategies

G.H.P Campmans,P.C Roos,N.R Van Der Sleen,S.J.M.H Hulscher

doi:10.1016/j.coastaleng.2021.103862

Abstract

Maintenance of navigation channels in shelf seas with tidal sand waves usually requires repeated dredging operations. Optimizing these interventions is a difficult task, particularly complicated by the nonlinear morphodynamics of sand wave recovery after dredging. Here we present a process-based model study, incorporating different strategies of dredging in an existing nonlinear sand wave model. We consider ‘topping’ (removing sand from crest) and ‘swiping’ (same, but now placing it in the troughs), for a range of dredging depths. Starting point is a fully developed sand wave or sand wave field, as simulated in the model. Results indicate that sand wave recovery is slowest after swiping. Also, larger dredging volumes imply longer recovery times. Next, we study the maintenance intervals and (cumulative) dredging volumes resulting from adopting a typical temporal strategy: swipe to a prescribed dredging depth, as soon as the recovering sand wave crests have reached a critical depth. Maintenance intervals are found to depend on the dredging depth and, importantly, to vary over time, as well. This last result shows that sand wave recovery depends not only on height, but also on its shape, emphasizing the limitations of existing, empirical (Landau-type of) models based on amplitude (or height) only.

Highlights

Tidal sand waves are rhythmic bed forms that are observed in various sandy tide-dominated shelf seas, such as the North Sea (Damen et al, 2018)
The sand wave crests form the highest points in the seabed topography, which may pose a threat to the least navigable depth guaranteed in shipping lanes (Katoh et al, 1998)
In our model study the guaranteed channel depth is denoted by Dmin and the design dredging depth by Ddd, see Fig. 3

Summary

Introduction

Tidal sand waves are rhythmic bed forms that are observed in various sandy tide-dominated shelf seas, such as the North Sea (Damen et al, 2018). They have wavelengths of hundreds of meters, heights of several meters and can typically migrate with several meters per year (Terwindt, 1971), in some cases much faster (Harris, 1989). The sand wave crests form the highest points in the seabed topography, which may pose a threat to the least navigable depth guaranteed in shipping lanes (Katoh et al, 1998).

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Conclusion